Generally speaking, there is more vibration in diesel engines though some of the latest European diesel cars have smoother and quieter engines. Over a long period of time, the extra vibration rattles up the car as a whole. And when cladding wears out with time the sound and vibrations worsen. Also, diesel engines require extra care compared to gasoline engines. If that extra care is not given, the engine emissions start increasing and this is the reason for the smell. This is why small children feel nausea if they are made to travel in diesel vehicles over extended periods especially on hilly roads.
